It is well-known in the art to extend polymers such as polyurethanes. This extended material will then be designated for use in a desired area of utility. Typical of such extending agents is mineral oil, such mineral oil extended polyurethanes being disclosed in U.S. Pat. Nos. 3,714,110 and 3,747,037.
It has also been determined that the mineral oil extended polyurethane is useful in the reclamation and protection of insulated electrical devices. Such devices may, for example, be underground telephone cables which are exposed to fluid contaminants. These contaminants can seriously impair the electrical and mechanical properties of such a device. The protectant material is pumped into the cable to remove water that has penetrated into interior free spaces. The material is pumped at low viscosity to achieve an appropriate distribution and it then cures in place to a high viscosity. The cured material acts as a hydrophobic barrier to subsequent water penetration. In another application, this material may be utilized as an encapsulant for sealing sections of cable. In this manner, the material serves to prevent, from the outset, the penetration of fluid contaminants.
A mineral oil extended polyurethane which is useful for this purpose is disclosed in U.S. Reissue Pat. No. RE 30,321. That patent defines a cured, cross-linked, mineral oil extended polyurethane prepared from specific polyurethanes and coupling agents, the latter being necessary to compatibilize the mineral oil with the cross-linking urethane elastomer.
Disadvantages of these mineral oil extended polyurethane systems were encountered, however, and these are described in U.S. Pat. No. 4,168,258. There it was stated that, with the earlier mineral oil extended polyurethanes, the mineral oil would tend to migrate toward any grease present in the cable or device in order to be reclaimed or encapsulated. This grease is encountered more frequently in newer insulated electrical devices. This migration was shown to cause the formation of an oily film at the grease interface which tended to decrease the reclamation and encapsulant effectiveness of the polyurethane. In order to avoid these difficulties, the patent specifically defined a polyurethane-mineral oil-coupling agent formulation relying on the presence of a polydiene moiety in the polyurethane structure. Mineral oil remained as the extending agent, with the stated preference for including some aromatic carbon content therein.
It is also known that previous polyurethane compositions have been difficult to re-enter after they have fully cured primarily due to their high cast strength and aging hardness, as well as due to their opaque or cloudy color. The high cast strength and hardness of these prior art polyurethanes contribute to the difficulty of cutting through or removing cured material from a repaired area. In some applications, the opaque color makes it difficult for the operator to establish the exact location to reenter a repair. For these reasons, clear, soft polyurethane gels are preferred. With either the clear or opaque products, the ability of these polyurethanes to be easily reentered is important in the repair or encapsulation of insulated electrical or telephone cables when a second splice or connection must be made in the same area as the previous repair or encapsulation. There are also situations where the initial repair or encapsulation is improperly made and has to be re-done. For these reasons, the primary concern regarding the physical properties of these gels is to provide a polyurethane having a relatively low tear strength and hardness. Furthermore, it is highly desirable for these materials to maintain these properties over time.
A vegetable oil extended polyurethane which satisfies some of these requirements and provides an initially reenterable gel is disclosed in U.S. Pat. No. 4,375,521. There, vegetable oil extended polyurethanes of a three component system comprising a specific polyurethane, vegetable oil, and specific extending agent is disclosed for use in reclamation and encapsulation applications. However, these vegetable oil extended formulations usually provide opaque gels, and, more importantly, tend to cause cracking or stressing of the polycarbonate connectors which are usually present in the cable unit being reclaimed, encapsulated, or repaired. Furthermore, some of these gel formulations age harden over time to make reenterability difficult.
In U.S. Pat. No. 4,355,130, a polyalphaolefin extended polyurethane is disclosed which resolves the stress cracking problem. Such polyalphaolefin extended polyurethanes comprise specific polyurethanes, a specific polyalphaolefin extender, and, for reclamation and encapsulation purposes, specific ester coupling agents. The coupling agent is required to compatibilize the formulation so that there will be no "spewing" of extender from the cured material.
Generally, the use of high amounts of such coupling agents tends to reduce the electrical characteristics of the gels. This is due to the presence of ester or other polar groups within the polyurethane structure. When such polyurethanes are used for the repair or encapsulation of electrical devices, they are unable to restore the same electrical characteristics because of their higher dissipation factors. Also, such formulations are not compatible with cable grease and the polyalphaolefin would tend to migrate toward any such grease present in the cable or device to be repaired or encapsulated.
U.S. Pat. No. 4,533,598 issued Aug. 6, 1985 discloses extended polyurethanes which provide soft, reenterable gels having excellent electrical characteristics. These gels comprise a polyurethane which is extended with a liquid cyclic olefin. However, these compositions have limited compatibility with cable grease.
Thus, while the art described in the above patents represents a progression in the technology of reenterable encapsulants, none satisfactorily solves the problem of compatibility with cable grease. When the state of the art encapsulants are in contact with cable greases, an incompatibility develops as evidenced by an exudation of a liquid either from the grease or the encapsulant. In some cases, the liquid interface may result from migration of liquids from both the encapsulant and the grease. It has been demonstrated that the presence of a liquid interface between the cable grease and the encapsulant will provide a leak path for water or contaminants. The presence of such contaminants then leads to the failure of the electrical devices by corrosion.